1. Field of Invention
The present invention relates to an electrothermal vaporization atomic fluorescence spectroscopy and spectrometer for determination of Cadmium.
2. Description of Related Arts
Owing to the sewage irrigation in large quantities and abuse of fertilizer, China suffers severe Cadmium (Cd) pollution, with some areas having reached the point of producing “Cadmium rice”. For example, in a sewage-irrigated local site of city Shenyang, the Cd concentration in the locally-produced rice was as high as 0.4-1.0 mg/kg, which have reached or exceeded the average “bone pain illness”-inducing Cd concentration. In view of this, the technology for quick determination of Cd has in recent years attracted wide attention, and has developed a series of quick measuring methods based on biosensors, colorimetry, enzyme inhibition, electrochemistry and atomic spectrum, etc. However, most of these methods can only determine the heavy metal ions in solution, and still can't avoid the time-consuming and laborious sample pre-treatment process; and as a result of matrix interference it is difficult to achieve accurate measurement, leading to high false-reporting rates. Although it can be achieved in great degree to simplify the heavy metal measurement for soil and agricultural products, it can't completely solve this difficult problem. The way to really realize direct determination of heavy metals in soil and agricultural products is nevertheless the atomic spectral methods which use Electrothermal Vaporization (ETV) or Laser Ablation (LA) as the means of sample introduction. Among the atomic spectral methods, the relatively mature techniques of Electrothermal Vaporization-Inductively Coupled Plasma Optical Emission Spectrometry (ETV-ICPOES), Mass Spectrometry (ETV-ICPMS) or Graphite Furnace Atomic Absorption Spectroscopy (GFAAS) have all been reported in use for the measurement by direct sampling. With the development in background correction technology and continuous light source technology, the direct sampling technique using electrothermal vaporization is more and more approaching real application. However, for the application in the field of quick determination for soil and agricultural products, although the above-mentioned technologies can inhibit the matrix interference to a certain degree, it is still difficult to fully overcome the problem, and it remains an unsolved problem for more complex matrices. Therefore, when using electrothermal evaporation as the means of sample introduction, the above-mentioned detection problem is practically to develop a method to eliminate the matrix interference, so as to meet a variety of complex matrices.
Atomic Fluorescence Spectroscopy (AFS) is a relatively rapidly developed atomic spectroscopy technique in China, which can use dispersion-free measurement thanks to its simple spectra and less spectra overlapping of atomic fluorescence. This greatly simplifies the instrument structure, makes it easy to realize miniaturization, and gives the possibility to be used in field measurement. But the currently commonly-used atomic fluorescence spectrometers use the Hydride Generation (HG)-based sample introduction technique. What have been reported in the literature about the electrothermal vaporization atomic fluorescence spectrometer include the measurement of Lead in solution by using graphite furnace as the evaporation and atomization device, and the measurement of heavy metals in solution after being digested by using Tungsten Coil (TC)-based Electrothermal Evaporation-Atomic Fluorescence Spectroscopy (ETV-AFS). Although these two types of device mentioned above possesses the potential of direct sampling by using ETV, it is still difficult to completely solve the matrix interference problem.
Matrix interference has been a major problem puzzling the atomic spectroscopy using direct sampling. Although the problem can be alleviated after matrix correction, it can't fundamentally solve the problem, and it is necessary to figure out a way otherwise. The development of the solid Mercury measurement technique based on atomic absorption since the 90s of last century provides a good inspiration. This technique carries out the measurement as follows: first release the Mercury in atomic form while decomposing the organic matter by oxidation through sample combustion in pure oxygen or air and further catalytic combustion; then separate the atomic Mercury from the matrix after being captured by Gold-bearing adsorption agent; and finally reheat the adsorbent to release the captured Mercury and introduce it into the atomic absorption spectrometer by carrier gas for measurement. This technique realizes the separation of Mercury from its matrix by using a highly selective noble metal capture trap, thereby completely eliminating the matrix interference. This shows that the on-line trapping technique should be a very efficient means for eliminating matrix interference. When used for Cd measurement, as currently reported in the literature, the on-line trapping technique can in most cases only capture hydrides or free atoms formed in the flame, while the capture of Cd introduced by electrothermal vaporization has not yet been reported. This is mainly due to the reason that, under normal conditions, the Cd formed by electrothermal vaporization exists mostly in the form of nanoparticles, which can't be efficiently trapped.